1. Field of the Invention
This invention relates to wire and cable. In one aspect the invention relates to flexible wire and cable coverings, articles and accessories while in another aspect, the invention relates to olefin multiblock copolymer compositions from which flexible wire and cable coverings are made.
2. Description of the Related Art
Flexible, electrically semiconductive compounds are desired in many applications, for example wire and cable, industrial belts (anti-static), printing rollers, etc. In wire and cable applications, flexibility is desirable for ease of reeling and, also, handling during installation. Also, in some applications, such as in industrial cables and cords, flexible cables are required.
Wire and cable accessories are other applications in which flexibility is important, e.g., molded or extruded parts used to connect or terminate cables. In these applications flexibility is highly desirable for ease of installation.
To achieve the desired flexibility, generally elastomeric materials, such as ethylene-propylene-diene monomer (EPDM) and other olefin elastomers, synthetic rubbers, silicone rubbers and their various blends are used. In order to achieve the desired volume resistivity for any given application and, critically, for this volume resistivity to remain stable under operating conditions, a high loading of carbon black is typically needed. For example, in wire and cable applications generally a volume resistivity value of less than (<) 1000 ohm per centimeter (ohm-cm) and, preferably, <500 ohm-cm, is required. This requires a high loading of conductive carbon black, e.g., 35% wt. or higher. As mentioned, this is to establish a stable conductive network, which would lead to stable conductivity during operation of the power cable.
Of continuing interest is a semiconductive compound exhibiting a low volume resistivity (<500 ohm-cm) which remains stable under aging conditions with minimal carbon black loading so as to maintain desired material flexibility.